Scientists believe that meltwater beneath Mars’ ice could potentially support microbial life.
Although no evidence of life on Mars has ever been found, a new NASA study suggests that microbes might be able to survive under frozen water on the planet’s surface.
Through computer models, the study’s authors have shown that the amount of sunlight that can penetrate through water ice would be sufficient for photosynthesis in shallow pools of meltwater beneath the ice surface. Similar water pools that form within ice on Earth are found to be teeming with life, including algae, fungi, and microscopic cyanobacteria, all of which derive energy from photosynthesis.
“If we want to find life somewhere in the universe today, Mars’ icy regions are probably one of the most accessible places to investigate,” says lead researcher Aditya Khuller from NASA’s Jet Propulsion Laboratory in Southern California.
Mars has two types of ice: frozen water and frozen carbon dioxide. In their research, published in Nature Communications Earth & Environment, Khuller and his colleagues focused on water ice. Large quantities of this formed from snow, mixed with dust, that fell on the surface during a series of Martian ice ages over the past million years. This ancient snow has since transformed into ice, which still contains dust particles.
While dust particles can darken light in the deeper ice layers, they are crucial to understanding how underground meltwater pools can form. Dark dust absorbs more sunlight than the surrounding ice, which can lead to warming and ice melting up to several meters below the surface.
Meltwater as a potential source of life The white edges along channels in Mars’ Terra Sirenum are thought to consist of dusty water ice. Scientists suspect that meltwater could form under this type of ice, providing a place for possible photosynthesis. This is reinforced by NASA’s color images, although the blue tints in the images would not be visible to the human eye.
Mars scientists disagree on whether ice can actually melt when exposed to Mars’ surface. This is due to the planet’s thin, dry atmosphere, where water ice would likely sublimate—transition directly into gas, like dry ice on Earth. However, the atmospheric conditions that make surface melting difficult would not apply beneath a dusty snow layer or glacier.
Vibrant micro-ecosystems On Earth, dust in ice can form so-called “cryoconite holes”—small cavities in ice that form when dust particles absorb sunlight and melt deeper into the ice. These dust particles eventually stop sinking but still generate enough heat to create a meltwater pocket around them, supporting a thriving ecosystem of simple life forms.
“This is a common phenomenon on Earth,” says co-author Phil Christensen from Arizona State University. “Dense snow and ice layers can melt from within, with sunlight penetrating and warming it like a greenhouse, rather than melting from above.”
Christensen has studied Mars ice for decades and leads the operations of a heat-sensitive camera called THEMIS aboard NASA’s 2001 Mars Odyssey probe. In previous research, Christensen and Gary Clow from the University of Colorado Boulder demonstrated through models how liquid water could form in dusty snow layers on Mars. This research formed the basis for the new study, which focuses on the possibility of photosynthesis on Mars.
In 2021, Christensen and Khuller jointly published research on dusty water ice visible in Mars’ gullies. They proposed that many of these gullies form through erosion caused by melting ice forming liquid water.
The new research suggests that dusty ice allows enough light for photosynthesis up to 3 meters below the surface. In this scenario, the upper ice layers prevent shallow meltwater pools from evaporating while also providing protection from harmful radiation. This is important because Mars, unlike Earth, lacks a protective magnetic field to shield it from both solar and cosmic radiation.
According to the researchers, the water ice most likely to form underground pools would be located in Mars’ tropics, between 30 and 60 degrees latitude, in both the northern and southern hemispheres.
Khuller hopes to soon recreate Mars’ dusty ice in a laboratory to study it up close. Meanwhile, he and other scientists are beginning to map the most likely locations on Mars where shallow meltwater can be found—potentially important targets for future human and robotic missions.
